210 dr. a. jowett ox the [June 1914* 



Lancashire was postulated by Mr. R. H. Tiddeman, 1 who pointed 

 out the diversion of the ice-drainage of the Lime and Ribble basins 

 consequent upon the obstruction of its natural outlet by the ice 

 from the Lake District. The Ribblesdale ice thus had a tendency 

 to escape eastwards across the Pennines wherever suitable gaps 

 presented themselves ; and we find, in addition to the great flow 

 of ice into Airedale, north of Boulsworth Hill, small ice-lobes 

 crossing the watershed at Widdop and at Gorple and a larger 

 stream flowing into Upper Calderdale. It is worthy of note that 

 there is, broadly speaking, a gradual decrease in height of the 

 Drift-limits marked on the map as one proceeds in the direction 

 in which the Drift was carried, a fact which is in itself a strong 

 argument in support of the glacial origin of the Drift. 



A detailed examination of the Drift-limits in their relation to 

 the surface-features will reveal many illustrations of the general 

 principle 2 that obstacles in the path of an ice-stream tend to 

 retard its movement and to limit its extension, the level of the 

 ice being usually raised higher in front of an obstacle and depressed 

 on its lee side. The best examples occur in the Upper Irwell basin, 

 as its hills are high enough never to have been deeply covered, even 

 when the ice attained its maximum thickness. The complementary 

 principle that deep narrow valleys tend to control and direct the 

 movements of the ice within their confines is also well illustrated, 

 and for the same reason — although there is good evidence that, 

 when the ice was of sufficient thickness, its upper layers moved 

 along in the general direction of ice-movement, shearing over the 

 more restricted currents below. It is clear, however, that in this 

 area we are recording conditions which hampered the movements 

 of the ice so much that its chief function was deposition, erosion 

 being reduced to a minimum. 



The high ground north and north-east of Bacup was crossed by 

 the Ribblesdale ice, though apparently never in sufficient quantity 

 to give rise to a strong southward-moving stream. Lower gaps, 

 however, occur on the west, and through them definite streams 

 of Ribblesdale ice flowed down the Whitewell-Brook and Limy- 

 Water valleys. Along with this southward to south-westward flow 

 of the Ribblesdale ice there was a movement of the North- Western 

 ice along the valley from Accrington to Burnley, as shown by 

 the gradual fall of the North- Western Drift-limit along the steep 

 northward slope of the ridge from Great Hameldon eastwards. The 

 North- Western ice appears to have crossed this ridge only as a 

 small lobe through the gap at the head of the Limy- Water valley, 

 though a few boulders of igneous rocks have been found in the 

 Ribblesdale Drift in the Whitewell-Brook valley, and a small 

 isolated patch of North- Western Drift occurs at 1350 feet above 

 CD. on the watershed between the Whitewell-Brook and Upper 

 Irwell valleys. 



1 Q. J. G. S. vol. xxviii (1872) p. 487. 



2 P. F. Kendall, ' Supplementary Observations on the Glacier Lakes of 

 Cleveland' Proc. Yorks. Geol. Soc. n. s. vol. xv (1903) p. 43. 



